// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_DNS_DNS_CONFIG_SERVICE_H_
#define NET_DNS_DNS_CONFIG_SERVICE_H_

#include <map>
#include <memory>
#include <string>
#include <vector>

#include "base/macros.h"
#include "base/memory/scoped_vector.h"
#include "base/threading/non_thread_safe.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
// Needed on shared build with MSVS2010 to avoid multiple definitions of
// std::vector<IPEndPoint>.
#include "net/base/address_list.h"
#include "net/base/ip_endpoint.h" // win requires size of IPEndPoint
#include "net/base/net_export.h"
#include "net/dns/dns_hosts.h"

namespace base {
class Value;
}

namespace net {

class IPAddress;

// Default to 1 second timeout (before exponential backoff).
const int64_t kDnsDefaultTimeoutMs = 1000;

// DnsConfig stores configuration of the system resolver.
struct NET_EXPORT_PRIVATE DnsConfig {
    DnsConfig();
    DnsConfig(const DnsConfig& other);
    virtual ~DnsConfig();

    bool Equals(const DnsConfig& d) const;

    bool EqualsIgnoreHosts(const DnsConfig& d) const;

    void CopyIgnoreHosts(const DnsConfig& src);

    // Returns a Value representation of |this|. For performance reasons, the
    // Value only contains the number of hosts rather than the full list.
    std::unique_ptr<base::Value> ToValue() const;

    bool IsValid() const
    {
        return !nameservers.empty();
    }

    // List of name server addresses.
    std::vector<IPEndPoint> nameservers;
    // Suffix search list; used on first lookup when number of dots in given name
    // is less than |ndots|.
    std::vector<std::string> search;

    DnsHosts hosts;

    // True if there are options set in the system configuration that are not yet
    // supported by DnsClient.
    bool unhandled_options;

    // AppendToMultiLabelName: is suffix search performed for multi-label names?
    // True, except on Windows where it can be configured.
    bool append_to_multi_label_name;

    // Indicates that source port randomization is required. This uses additional
    // resources on some platforms.
    bool randomize_ports;

    // Resolver options; see man resolv.conf.

    // Minimum number of dots before global resolution precedes |search|.
    int ndots;
    // Time between retransmissions, see res_state.retrans.
    base::TimeDelta timeout;
    // Maximum number of attempts, see res_state.retry.
    int attempts;
    // Round robin entries in |nameservers| for subsequent requests.
    bool rotate;
    // Enable EDNS0 extensions.
    bool edns0;

    // Indicates system configuration uses local IPv6 connectivity, e.g.,
    // DirectAccess. This is exposed for HostResolver to skip IPv6 probes,
    // as it may cause them to return incorrect results.
    bool use_local_ipv6;
};

// Service for reading system DNS settings, on demand or when signalled by
// internal watchers and NetworkChangeNotifier.
class NET_EXPORT_PRIVATE DnsConfigService
    : NON_EXPORTED_BASE(public base::NonThreadSafe) {
public:
    // Callback interface for the client, called on the same thread as
    // ReadConfig() and WatchConfig().
    typedef base::Callback<void(const DnsConfig& config)> CallbackType;

    // Creates the platform-specific DnsConfigService.
    static std::unique_ptr<DnsConfigService> CreateSystemService();

    DnsConfigService();
    virtual ~DnsConfigService();

    // Attempts to read the configuration. Will run |callback| when succeeded.
    // Can be called at most once.
    void ReadConfig(const CallbackType& callback);

    // Registers systems watchers. Will attempt to read config after watch starts,
    // but only if watchers started successfully. Will run |callback| iff config
    // changes from last call or has to be withdrawn. Can be called at most once.
    // Might require MessageLoopForIO.
    void WatchConfig(const CallbackType& callback);

protected:
    enum WatchStatus {
        DNS_CONFIG_WATCH_STARTED = 0,
        DNS_CONFIG_WATCH_FAILED_TO_START_CONFIG,
        DNS_CONFIG_WATCH_FAILED_TO_START_HOSTS,
        DNS_CONFIG_WATCH_FAILED_CONFIG,
        DNS_CONFIG_WATCH_FAILED_HOSTS,
        DNS_CONFIG_WATCH_MAX,
    };

    // Immediately attempts to read the current configuration.
    virtual void ReadNow() = 0;
    // Registers system watchers. Returns true iff succeeds.
    virtual bool StartWatching() = 0;

    // Called when the current config (except hosts) has changed.
    void InvalidateConfig();
    // Called when the current hosts have changed.
    void InvalidateHosts();

    // Called with new config. |config|.hosts is ignored.
    void OnConfigRead(const DnsConfig& config);
    // Called with new hosts. Rest of the config is assumed unchanged.
    void OnHostsRead(const DnsHosts& hosts);

    void set_watch_failed(bool value) { watch_failed_ = value; }

private:
    // The timer counts from the last Invalidate* until complete config is read.
    void StartTimer();
    void OnTimeout();
    // Called when the config becomes complete. Stops the timer.
    void OnCompleteConfig();

    CallbackType callback_;

    DnsConfig dns_config_;

    // True if any of the necessary watchers failed. In that case, the service
    // will communicate changes via OnTimeout, but will only send empty DnsConfig.
    bool watch_failed_;
    // True after On*Read, before Invalidate*. Tells if the config is complete.
    bool have_config_;
    bool have_hosts_;
    // True if receiver needs to be updated when the config becomes complete.
    bool need_update_;
    // True if the last config sent was empty (instead of |dns_config_|).
    // Set when |timer_| expires.
    bool last_sent_empty_;

    // Initialized and updated on Invalidate* call.
    base::TimeTicks last_invalidate_config_time_;
    base::TimeTicks last_invalidate_hosts_time_;
    // Initialized and updated when |timer_| expires.
    base::TimeTicks last_sent_empty_time_;

    // Started in Invalidate*, cleared in On*Read.
    base::OneShotTimer timer_;

    DISALLOW_COPY_AND_ASSIGN(DnsConfigService);
};

} // namespace net

#endif // NET_DNS_DNS_CONFIG_SERVICE_H_
